The two don't quite coincide. WoT predates the "net" by about 6 years, the "web" wasn't much before 1996, and the pre web dialup internet bbs were not nearly prevalant enough for any real impact IMHO.
Speaking for myself, I discovered WoT when tEotW came out in pb in late 1990. I was well and truly hooked (and I don't consider myself unique) long before I even thought of looking for sites on the web. I'm fairly certain that wotmania was one of the first 'fan sites' and it came along in 1999 IIRC, long after the series had established itself.
The internet may have helped some, it also may have hurt, check out Amazon's reviews of CoT, I don't think anybody can generate any kind of specific numbers that kind of negative publicity generates, but it probably isn't 0.
My best guess is that the internet has has some impact, but no more on WoT than any other fantasy series, and probably not all that much as a general rule. As someone else mentioned, LotR was wildly popular w/o the internet (or the movies, everyone in my family read and re-read it multiple times by the late 60's) And my brother-in-law and myself both became hooked on WoT long before our computers were anything other than something to write reports and do spreadsheets on (anyone remember Lotus 123?)

NaCl(WoT would still be a best seller)H2O